The first to appear was the full-size or 1FF (1st Form Factor), the size of a credit card (85.60 mm × 53.98 mm × 0.76 mm). It was followed by a mini-SIM or 2FF (2nd Form Factor), which has the same thickness but is 25 mm long by 15 mm wide, with one of its corners cut to prevent misinsertion. Next came micro-SIM or 3FF (3rd Form Factor), with dimensions of 15 mm × 12 mm.

In 2012 the nano-SIM or 4FF (4th Form Factor) was introduced, which measures 12.3 × 8.8 × 0.67 mm. Nano-SIM cards can use adapters to gain compatibility with devices with Micro-SIM and Mini-SIM slots. A Micro-SIM card can also be fitted in Mini-SIM slot with an adapter.Specification